No Cat=Bad mileage???

I was in my shop class today and some kid told me that my trucks getting such bad mileage because is because I gutted the cat on it. He said something about the "hydrocarbons returning to the not burned fuel" or something. Didn't sound right to me, I always though that if its done right and you dont have the O2 sensors and crazy computer and all (old truck) that it would run better and have better mileage because of the less restriction in the exhaust system. Maybe I heard wrong, so im just curious on the hard facts here.

i've gutted a few catylitic converters and never lost any gas mileage. ask your shop teacher...

he's confusing your cat with the egr i think.

cat is for emissions only.. gutting it will only reduce backpressure.. I dont thik it'l affect fuel economy good or bad

I was in my shop class today and some kid told me that my trucks getting such bad mileage because is because I gutted the cat on it. He said something about the "hydrocarbons returning to the not burned fuel" or something. Didn't sound right to me, I always though that if its done right and you dont have the O2 sensors and crazy computer and all (old truck) that it would run better and have better mileage because of the less restriction in the exhaust system. Maybe I heard wrong, so im just curious on the hard facts here.Modern engines are designed for optimal airflo / cam valve relationships with the cat in line. Removing the cat will hurt your off the line acceleration, and for the people that need to worry about it......... your gas mileage..§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§REFUSE TO LOSE§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§

if your o2 sensor is before your cat then it shouldn't effect your gas mileage, if it's after then it probably will.

my cats have been taken off and I get about 22mpg (premium fuel and a couple cheap intake mods) in my 97 LT1

i have no cat on my mustang with off road hpipe, my car sucks gas like you wouldnt beleive, worse then any v8, and it only a 6. be be honest with you, i been drive about an hours and half down to jersey to see my gf at college and for some reason it seem good one gas with me doing 75-85 the whole way. but i know around town it sucks, and yes your off the line sucks. i lost some much, im putting my y pipe with cat backs on witha cat back system as soon as i get cought up on my bills. hey sell high flow cats. i think i told you think b4. i may have been someone else, i dont remember. id leave there and dont worry about it. if you want to gain power, do other stuff. that little shit most ppl dont even bother. but it ups to you

wholly shit where did 92RS come from????

lol, but yeah, hes spot on, if you have a post cat 02 sensor and dont have a simulator on it, then the lack of a cat will cause the engine to run improperly, but then i would have assumed it would run leaner rather than ritcher, so your performance would suck, but you gas mileage should have been higher if anything. i woul start looking at other things, what kinda shape is your air filter in? last time you had a tune up? that kinda stuff.

My sensors are before the cat. I just replaced the air and fuel filter less than a week ago. New plugs, cap, and rotor. And we tore it apart and put in new gaskets, pushrods, and fixed one of the springs that broke. The only thing I can think of is the timing, since we just threw the distributer back on when we were done and set it to whatever sounded right heh. I had a VERY bad gas and oil leak when I first baught it, but since I fixed the gas leak, and the oil leak isn't as bad as before, but still goes through a quart every few weeks. The timing isn't that bad, but would just that be the problem? I seriously go through $60+ a WEEK just going to school and work and back, hardley use it for anything else.

*smacks forhead with lead pipe* and you didnt mention that before why????? set your timing douche bag ;)

lol. I know the timing is off, but it runs fine for it not being right. It's not that far off, but even if it's off like 1 degree or something, that can really give you that bad of mileage? Anyways, I just heard him talking about cats and how they give you bad mileage if you gut them out with any car period. I was just wondering if it does or not haha.

hahaha douche bag

The only effect I had after I took the cat off is my exhaust makes your eyes water lol... Seriously though, you can tell if you are driving behind a car without one!

I happen to enjoy that smell. :smile:

it may significantly shorten your life-span, but i love it. i sit behind my car with it running before i go out at night, and when girls ask what my cologne smells like, i tell them "like man"...

wow, where are the girls at, the testosterone in here is making it hard for ME to breath ;)

wait a sec...
89 cant breathe
89 steps down as mod
leadership void develops
i become mod
i rule forum with an iron fist
camaro forum takes over all other forums...

we're already taking over

i told you about this before 92..prolly dont remember but the guys at a local chevy dealer told me that my lack of cats on a 305 tpi is giving me a rich problem. still havent got any on, i like the sound but it seems my plugs foul out every so often. is that related at all?

we're already taking over

yes, but not violently enough...

Anywho...I have looked up information on at least 3 dozen websites about removing your cat or gutting it and how it really effects the car. They all say totally different things though. The cat on my truck is removed right now, so the exhaust is coming right from the downpipe. The tubing on the left manifold bends and goes over to the passenger side tubing, so they are unequal length. Does this do anything important? When I am at a stop it sounds normal, really loud, but normal for like a second and a half, then it resonates or something and sounds like I have my bass up really high, and shakes the whole truck, then back and forth. Is this because of the almost zero backpressure, and the gasses going back up into the tubing, or the unequal length of the tubing er wha? Im also wondering why it is running so rich without it now, im getting HORRIBLE mileage. My sensors are before the cut, so I don't know why it would. Also, to clear things up once and for all, Does removing the cat add any power or torque, or have any advantage at all??? Everyone is saying different things about it, so I would like to know the facts. The dozen or so sites I looked at are all totally diferent so it would be nice to konw. Thanks for the knowledge! :biggrin:

still wondering the same thing...about the power, i have heard from a lot of people that it can add a few horses on v8's, and on four bangers it only results in too much of a reduction in back pressure. in other words that due to the displacement of a v8 it can benefit somewhat from removing the cats. whether thats true or not i have no clue.

we're already taking over
ya we must take over the other sections by more posts and more activity in camaro section, one day we might beat off-topic(yeah right)

I think as long as you add a free flowing exhaust system when you take the cats of it will help out. But taking them off on a stock system is pointless.

i removed the cat on my car, i have o2 sensors before the cat, and my car is fine.. the exhaust doesnt smell bad, it kicks hard off the line, and the car actually sounds a little meaner.. :)

Why would my mileage be so bad though? It runs REALLY rich, but my o2 sensors are behind the cut...

EDIT: Would the richness be caused by the short system? I have it dumping out about 2 feet from the right manifold, and maybe 4 from the drivers manifold, since it has to curve over and go into the right ones tubing. After I drive a while, I can smell the gas just from the converter being removed, but I can also smell this extra gas smell...and when I take the air filter off and open the TB valves smoke pours out of them and smells like gas really bad. Why would it run so rich with the sensors behind the cut!? GAH!

if your sensors are behind the cat and you have the exhaust coming out before the sensors then the computer cant get a readout on the exhaust.. which will cause the car to put more gas into the mix, and more gas at a time means less time the gas will be there.. an easy fix would be to get a high flow cat if you have post converter sensors.. because a high flow cat would give you the open flow you want, but wont rob you..

*im no mechanic, but thats my understanding on how these things work*

oh, and 89.. all the girls are over here.. they say they'll be back later tonight...

My o2 sensors are before the cut. Like they have the exhaust go through it just like it would normally even with the cut. Like this, exhaust manifolds, then piping, then the sensors, then the cut and it just dumps there. If the sensors are behind the cut wouldnt they get the same reading since the cut is after it? and is that even the problem? gah im sick of getting 2 mpg haha.

My sensors are before the cat as in the exhaust dumps out after it reaches the sensors.

alright i follow ya. but i have to wonder, you're saying that as fast as the exhaust is traveling through the pipes, the small space that the cat takes up would cause a false reading if the sensors are behind it, but not before? i mean if they're before the cats that's what a foot or so difference and without cats they would read it right but if they're after the cats it reads wrong? not trying to make you sound like an ass it just doesn't make a lot of sense to me, that has to be a really sensitive sensor if that's the case, and if these problems are caused by no cats then im guessing there are two different sensors, one used in front of the cats, which makes no difference if there's cats on or not, and one used behind the cats which would cause these problems by not having cats. see what im sayin?

lol sorry my posts were confuzing. I was simply asking why im getting such bad mileage ever since i cut the cat off. My sensors are on the manifolds, meaning they read the same exhaust with the cat on or off. My trucks running really rich since i took the cat off, but before it didnt. I was wondering what else would cause it to run rich by only taking the cat off, because it cant be the o2 sensors. sorry bout the confuzion.

i thought you were saying you had sensors before and after.. like in many of the newer 4th gens.. cutting the cat off will desrease the ammount of backpressure your car produces.. i think the decrease in backpressure causes the car to run rich like that.. but i dont think it should have that much of an effect..

Sorry about that. Would welding in just a straight pipe fix that, or will the abcense of the cat still make it all goofy like that? Anything I could do to fix it without buying a new cat, or welding in a new pipe? Im welding in a pipe friday anyways, but im just wondering. Thanks.

I pulled my nasty cat off and am getting a high flow catco to throw on it but in the mean time while it's been off , I haven't noticed anyless performance from my engine or drivability. I do however feel like I need a pair of ear plugs and a seat with shock absorbers as it's loud as hell and shakes the shit out of everything.

You can get some cheap cat's from like autozone or off ebay , Ebay has one for like 35 dollars to buy it now a universal GM fit. anywhere from 1 7/8 I-D / O-D to 3 I-D / 3 O-D

I'm back =D

good to have you back, I missed lookin at your car.

The only effect I had after I took the cat off is my exhaust makes your eyes water lol... Seriously though, you can tell if you are driving behind a car without one!Try working on something when you're near a nitro-funny idling and keeping you're eyes from watering..§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§REFUSE TO LOSE§§§§§§§§§§§§§§§§§§§§§§§§§§§§§§